A heart is the center of a person's circulatory system. It includes a complex electromechanical system performing two major pumping functions. The heart includes four chambers: right atrium (RA), right ventricle (RV), left atrium (LA), and left ventricle (LV). The left portions of the heart, including the LA and LV, draw oxygenated blood from the lungs and pump it to the organs of the body to provide the organs with their metabolic needs for oxygen. The right portions of the heart, including the RA and RV, draw deoxygenated blood from the body organs and pump it to the lungs where the blood gets oxygenated. These mechanical pumping functions are accomplished by contractions of the heart. In a normal heart, the sinoatrial (SA) node, the heart's natural pacemaker, generates electrical impulses, called action potentials, that propagate through an electrical conduction system to various regions of the heart to excite the muscular tissues of these regions. Coordinated delays in the propagations of these electrical impulses in a normal electrical conduction system cause the various portions of the heart to contract in synchrony to result in efficient pumping functions. A blocked or otherwise abnormal electrical conduction system and/or a deteriorated myocardium cause asynchronized contraction of the heart. Consequently, the person suffers from poor hemodynamic performance, including poor pumping efficiency and diminished blood supply that is usable to satisfy the needs for normal metabolism of the organs.
The heart's electrical conduction system includes internodal pathways between the SA node and the atrioventricular (AV) node, the AV node, the His bundle (also known as the bundle of His, the AV bundle, and the Common bundle), and the Purkinje system including the right bundle branch (RBB) and the left bundle branch (LBB). In the normal heart, the electrical impulses generated from the SA node are conducted to the AV node through the internodal pathways. The propagation of the electrical impulses is delayed in the AV node. The His bundle conducts the electrical impulses from the AV node to the right bundle branch (RBB) and left bundle branch (LBB). The RBB and LBB then conduct the electrical impulses to the RV and LV, respectively, through the Purkinje system, resulting in the contraction of the ventricles.
Damages or depression of the AV node and/or His bundle, known as AV block, impairs the AV conduction, i.e., conduction of the electrical impulses from the RA to the RV and LV. AV block, depending on a degree or severity, can result in excessive delay in the AV conduction, partial blockage of the AV conduction (only some electrical impulses are conducted to the ventricles), or total blockage of the AV conduction (no electrical impulse is conducted to the ventricles). AV block can result from, for example, ischemia, acute myocardial infarction, intoxication, and inflammation. Ablation of the AV node, a surgical procedure performed on patients with atrial fibrillation, also creates total blockage of the AV conduction.
Pacing therapy can restore cardiac function impaired by AV block. One method is His bundle pacing, i.e., delivery of pacing pulses to the His bundle. If conduction system below the AV node remains normal, pacing pulses delivered to the His bundle are conducted through the His bundle and the bundle branches to cause synchronized contraction of the ventricles. In addition, pacing of the His bundle prevents its degeneration, a pathological process that starts with severe or total AV block.
His bundle pacing requires locating a pacing site in or about the His bundle. Unlike conventional atrial and ventricular pacing sites, which can be located by imaging techniques such as fluoroscopy, His bundle cannot be reliably located by imaging. Additionally, chemical, biochemical, and biological therapies may provide further benefits to the condition of the AV node and/or His bundle, as well as other cardiac regions, in addition to His bundle pacing.
Therefore, there is a need for an improved method and system for delivering a therapy to the His bundle.